FR2676583A1 - METHOD FOR THE DESORTION OF FISSION IODINE. - Google Patents

Abstract

a) Process for the desorption of fission iodine, b) characterized in that a) ozone is used as the oxidizing gas, and b) the addition of the oxidizing gas is carried out at least in part, directly in the gas space above the solution. c) The invention relates to methods for the desorption of iodine from fission.

Description

The invention relates to a process for the desorption of fission iodine.

  process for the desorption of fission iodine from a solution containing nitric acid, nuclear fuels and / or fission products, wherein a) the solution is distilled

b) adding an oxidizing gas.

  Such a process is known from US Pat. No. 3,803,295. According to this method, fission iodine is extracted from solutions of nuclear fuels and / or fission products acidified with nitric acid, introducing in the solution, during the distillation of these solutions, gases

  oxidants such as ozone or oxides of nitrogen.

  Thus, non-volatile iodine compounds, such as iodides, but also organic iodinated compounds, are oxidized to volatile elemental iodine. In this way, the fission iodine can be extracted until the residual molarity is less than 2, 5 x

10-5.

  DE-C 2 29 51 339 discloses, furthermore, the extraction of fission iodine from

  from nuclear fuel solutions, by distillation under particular conditions, with simultaneous addition of nitrogen oxides.

  In the distillation of the solutions, there always appears a condensation of vapor in the gaseous space. The vapor condenses, either in a column of exchange of substances or in the condenser, or already at least partly, in the conduits above of the solution This condensate can reabsorb iodine extracted from the solution and reintroduce it into the solution The iodine absorbed in the condensate is then reduced again to iodide iodides are

  soluble at high concentrations in the condensate.

  This is one reason why iodine can not be eliminated quantitatively from these solutions The publications cited are not interested in this problem. The object of the invention is, therefore, to provide a more efficient method of the type mentioned at the beginning, in which in particular it is prevented that iodine already released from the solution in secondary processes is absorbed by the condensate,

  reduced and reintroduced into the solution.

  This object is achieved by the process according to the invention, characterized in that: a) ozone is used as an oxidizing gas and b) the addition of the oxidizing gas is carried out at least partly directly in the gas space above

of the solution.

  Unexpectedly, it turned out that the equilibrium of the iodine between the gaseous atmosphere and the condensate films on the walls of the container, behaves differently than when introducing gases into the solution. The fundamental difference is that the iodine and the introduced gases react fundamentally differently in the solution and in the condensate Its cause is the enormous difference of the degree of acidity The solution of the nuclear fuels and / or products of fission, is a strong nitric acid or concentrated, while the condensate consists of a very dilute aqueous solution (normally 0.01 0.1 M) of nitric acid Another difference comes from the fact that, in the known process, the gases have to a large extent already lost their oxidizing power after the passage of concentrated nitric acid This applies to

  oxides of nitrogen, but even more so to ozone.

  In the process according to the invention, the ozone used thus manifests its oxidizing activity only in the condensate, whereas in the known process, the gases which pass through the solution have, to a large extent, lost their oxidation power. ozone stream, introduced directly into the gaseous space above the solution, has the effect that the iodide dissolved in the condensate is reoxidized in iodine and, consequently, is no longer reintroduced into the solution, but , desirably, arrives in elemental form in the waste gas stream, where it can

  be retained almost quantitatively on filters.

  The amount of ozone introduced directly into the gas space is given, in the process according to the invention, by the requirement to shift the equilibrium

  redox I 2 / I-, in the condensate, on the side of I 2.

  In the publication "Untersuchen zur Jodanreicherung an Stahl und Ubergangsmetallen", (Studies of the concentration of iodine on steel and transition metals), Pt UB-Berichte, compendium of presentations on the occasion of the 1989 report of the project manager of university research on the nuclear fuel cycle, 8 and 9 May 1990, Pt UB 27, Kernforschungszentrum Karlsruhe, September 1990, pages 8 1-8 28, is certainly examined the mechanism of the adsorption of iodine in the condensate and on the walls of the container, during the dissolution and distillation of nuclear fuels or nuclear fuel solutions However, it is not proposed to introduce an oxidizing gas in the gaseous space above the solution. The advantage of the process according to the invention resides firstly in the fact that the fission iodine is almost quantitatively removed from the solution and the condenser. On the other hand, it is avoided that the parts of the installation which come into contact with the condensate be corroded during the

  reduction of iodine to iodide in the condensate.

  The invention is illustrated in more detail in the following, with the aid of an example of

production.

  By way of example, tests were carried out in order to simulate the conditions in a typical dissolver installation for nuclear fuels. A glass beaker (volume approximately 500 ml, internal diameter approximately mm) was heated in a thermostatic bath. to be closed with a Teflon lid In the Teflon lid there were slit-shaped openings into which metal test pieces of various types of steel could be inserted from inside. The metal test pieces were shaped 1-3 mm thick trapeziums with an exposed surface of 10 x 50 mm or were laid as 20 x 50 mm plates on pre-made slits. The solution mentioned at the beginning was simulated by a solution containing iodine, acidified with 25 to 50 ml of nitric acid The beginning of the test was pre-established (time t = 0) by introduction of this solution and rapid placement of the lid Iod vapors After the reaction time, the iodine concentration in the aqueous phase decreased relatively rapidly (half exchange time: 20 minutes). After the desired reaction time the condensation droplets of the metal specimens were collected in small sample glass containers or syringes to determine the concentration of iodine and iodide in the condensate. carried out comparative tests, in which ozone was introduced into the gaseous space

  above the solution at a speed of about 100 -

  mg / h In tests without introduction of ozone, an iodide concentration of approximately x 10-6 m in the condensate was found In the tests with introduction of ozone, the corresponding concentration, depending on the type of steel used ranged from 2 to 15 x -6 m.

Claims (1)

CLAIM   Process for the desorption of fission iodine from a solution acidified with nitric acid, containing nuclear fuels and / or fission products, in which a) the solution b) is distilled by adding an oxidizing gas characterized in that (c) ozone is used as an oxidizing gas, and (d) the addition of the oxidizing gas is carried out at least in part, directly in the gas space above of the solution.